In the conventional manufacturing process of a filter, network analyzers are generally used for measurements, and the center frequency of the filter is adjusted manually. In other words, after the filter is calibrated, the center frequency is fixed and cannot be adjusted by users anymore. Since the filter is packaged, the involved process is very complicated even though the filter can be unpackaged, adjusted, and re-packaged.
After purchasing the filter, purchasers have to send the filter to the original factory to calibrate the center frequency, thus causing tremendous inconvenience to manufacturers. In general, the filters are integrated into related communication equipments, and the filters must be removed from the communication equipments before they can be used as standalone devices. Obviously, such procedure is time-consuming and costly. In another situation, if the communication equipment is a communication base station, signal transmissions of the communication will be affected, or even the base station must be shut down during the process of removing the filters.
In view of the aforementioned drawbacks of the prior art, the present invention provides a tunable filter to overcome the aforementioned drawbacks.